A comparison of the lateral, Oxford and sitting positions for performing combined spinal-epidural anaesthesia for elective Caesarean section*

Authors

  • M. W. M. Rucklidge,

    1. Anaesthetic Research Fellow
    2. Current position: Consultant Anaesthetist, Department of Anaesthesia, Royal Devon and Exeter Hospital, Barrack Road, Exeter EX2 5DW, UK
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  • M. J. Paech,

    1. Associate Professor of Obstetric Anaesthesia, School of Medicine and Pharmacology, University of Western Australia, Perth, Australia; Department of Anaesthesia and Pain Medicine, King Edward Memorial Hospital for Women, 374 Bagot Road, Subiaco, Western Australia 6008, Australia
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  • S. M. Yentis

    1. Consultant, Magill Department of Anaesthesia, Intensive Care & Pain Management, Chelsea and Westminster Hospital, London SW10 9NH, UK
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  • *

    Presented in part at the Obstetric Anaesthetists' Association Annual Meeting, Cardiff, June 2003.

M. W. M. Rucklidge
E-mail: matthew.rucklidge@rdehc-tr.swest.nhs.uk

Summary

One hundred women were randomly allocated to the left lateral, Oxford or sitting position for induction of combined spinal-epidural anaesthesia for Caesarean section using 2.5 ml hyperbaric bupivacaine 0.5% and 10 μg fentanyl. Women in the left lateral were then turned to the right lateral position; women in the Oxford position were turned to the same position on their opposite side; and women in the sitting group were turned to the supine left tilt position. Women remained in these positions until ready for surgery, which was conducted in the supine position with a wedge placed under the right hip. Ephedrine requirements before re-positioning for surgery were less in the sitting position than in the other two positions: median (IQR [range]) doses for the lateral, Oxford and sitting groups were 21 (12–30 [6–48]), 18 (7.5–24 [6–48]) and 12 (6–21 [6–42]) mg, respectively; p = 0.04. Sensory block to touch sensation at the T5 dermatomal level was most quickly achieved in the lateral position with median (IQR [range]) block onset times for the lateral, Oxford and sitting groups of 9 (6–13 [4–30]), 15.5 (9–22 [4–34]) and 14 (9–18[6–36]) min, respectively; p = 0.004. In the Oxford position, more epidural catheters required dosing to achieve a sensory block of T5 before surgery: the number of patients (proportion) bolused in the lateral, Oxford and sitting groups was 1 (3%), 7 (22%) and 1 (3%), respectively; p = 0.01. We did not demonstrate any advantage in using the Oxford position for combined spinal-epidural anaesthesia for elective Caesarean section.

Combined spinal-epidural (CSE) anaesthesia for Caesarean section is associated with low failure rates and high acceptability [1]. Hypotension, however, is a common complication of spinal and CSE anaesthesia. It may be due in part to cephalad spread of local anaesthetic in the subarachnoid space and also aortocaval compression by the gravid uterus, with both these factors influenced by the parturient's posture during and immediately after subarachnoid injection. By influencing spread of local anaesthetic, maternal posture may affect the speed of onset of sensory block; however, studies of different maternal positions have produced conflicting results with respect to both haemodynamic stability and speed of onset of block [2–6].

Regional anaesthesia may be conducted with the parturient in the sitting or lateral position. A modification of the latter, the Oxford position, has also been described: by creating an upward slope in the thoracic region, and avoiding the supine position until just before surgery, it aims to protect upper thoracic nerve roots from exposure to local anaesthetic and to minimise aortocaval compression [7]. Studies investigating the effectiveness of this position are limited, conflicting and have all been conducted at the institution where the position was first described [5, 6].

In this randomised controlled trial, we compared the left lateral, sitting and Oxford positions at induction of CSE anaesthesia for elective Caesarean section, for their effects on haemodynamic stability and onset of sensory block.

Methods

The study took place at King Edward Memorial Hospital for Women, Perth, Western Australia. After approval by the local Research Ethics Committee and written informed consent, 100 women of > 38 weeks' gestation scheduled for elective Caesarean section were studied. Women with pre-eclampsia, diabetes mellitus, intrauterine growth retardation or multiple pregnancy were excluded.

Women were premedicated with ranitidine 150 mg orally the night before and the morning of surgery and all wore anti-embolic support stockings. Standard monitoring was attached (electrocardiography, pulse oximetry and non-invasive blood pressure), an intravenous cannula was inserted under local anaesthetic and 10 ml.kg−1 Hartmann's solution was administered. Women were randomly allocated using computer generated random numbers and sealed opaque envelope to the lateral, Oxford or sitting position. Women in the lateral group were placed in the full left lateral position with one pillow supporting the head. Women in the Oxford group were placed in the left lateral position, tilted slightly head down, with three pillows supporting the head and an air-inflated 3-litre intravenous infusion bag under the left shoulder. Women in the sitting position were positioned with their feet resting on a stool. Once positioned, a baseline systolic blood pressure was derived from the mean of three recordings taken from the left (lower if appropriate) arm while resting undisturbed. An intervention blood pressure was calculated based on a fall in systolic blood pressure of 20% or more from baseline. If resting baseline systolic blood pressure was 100 mmHg, then intervention blood pressure was considered to be 90 mmHg.

Combined spinal-epidural anaesthesia was performed in the midline with a needle-through-needle technique using an 18-G Tuohy/27G 27-gauge Whitacre CSE kit (Abbott Critical Care Systems, Sligo, Republic of Ireland). After infiltration with lidocaine, the epidural space was located with loss of resistance to saline at the L3/4 vertebral interspace. The spinal needle penetrated the dura mater with the distal aperture facing cephalad and, following clear flow of cerebrospinal fluid, 2.5 ml hyperbaric bupivacaine 0.5% (12.5 mg) and 10 μg fentanyl were injected over 30 s. An epidural catheter was then inserted 4 cm into the epidural space. Immediately after intrathecal injection, 6 mg ephedrine was given intravenously to all women. Once the epidural catheter was secured, parturients in the lateral group were immediately turned from the left to the full right lateral position, women in the Oxford position were turned 180° to lie in the identical right Oxford position and parturients in the sitting group were laid supine with a wedge placed under their right hip. They remained in these positions until sensory block was suitable for surgery, at which point they were laid supine with a wedge placed under the right hip.

Maternal non-invasive blood pressure was measured from the lower arm every minute from the intrathecal injection until surgery, then every 3 min until delivery and every 5 min thereafter. If the systolic blood pressure fell below the ‘intervention blood pressure’, ephedrine 6 mg was given intravenously. Additional fluid boluses of 200 ml crystalloid were given at the clinical discretion of the anaesthetist. A second anaesthetist assessed cephalad spread of sensory block every 3 min, using loss of light touch sensation with cotton wool. Loss of light touch at and including T5 bilaterally was considered adequate for surgery. If the block failed to reach this level 20 min after intrathecal injection, 5-ml increments of plain bupivacaine 0.5% were given via the epidural catheter until adequate block height was achieved. Times from intrathecal injection to completion of epidural catheter fixation, surgical incision, delivery and completion of surgery were recorded.

Oxytocin (Syntocinon®) 5 i.u. was slowly infused intravenously at delivery followed by 25 i.u. in 500 ml saline 0.9% over 4 h. Neonatal condition was assessed using Apgar scores at 1 and 5 min and umbilical cord gas analysis. At the end of surgery, the upper sensory level was checked and 500 mg naproxen given rectally. Patient-controlled epidural analgesia (PCEA) using 20-mg boluses of pethidine with a lockout interval of 15 min was provided and the time of first demand recorded.

The primary outcome was reduction in ephedrine requirements. Using data from previous studies, we calculated that a sample size of 30 patients per group would have 90% power at the 5% significance level to detect a difference in ephedrine requirement of 10 mg among groups. To allow for potential dropouts, 100 parturients were recruited. Secondary outcomes included time for sensory block to reach T5, level of highest sensory block, change in blood pressure, volume of fluid administered, neonatal condition and time to first demand for PCEA. Comparisons were made using Fisher's exact test for categorical variables, F-test for normally distributed variables and the Kruskal–Wallis test for noncontinuous variables and/or those with non-normal distributions. Times between spinal injection and onset of sensory block were compared using Kaplan–Meier survival analysis. An intention-to-treat approach was adopted for all analyses, which were performed using the SAS statistical package version 8 (SAS Systems, Cary, NC).

Results

Data were available from 96 of the 100 women. Three cases were excluded due to inadequate data collection and one was excluded shortly after induction of CSE anaesthesia due to the arrival of an emergency case in the theatre suite. Groups were comparable in age, height, weight and body mass index (Table 1). There was no difference in the time taken from insertion of the Tuohy needle to spinal injection and from spinal injection to catheter fixation, surgical incision, delivery, completion of surgery and first demand for PCEA (Table 2).

Table 1.  Characteristics of parturients undergoing Caesarean section under CSE in the left lateral, Oxford and sitting positions. Values are mean (SD) or number (proportion).
 Lateral
(n = 29)
Oxford
(n = 32)
Sitting
(n = 35)
Age; years33.3 (5.1)31.0 (4.7)30.3 (5.8)
Height; cm163.2 (7.0)162.3 (7.0)161.9 (7.8)
Weight; kg78.8 (14.6)76.4 (11.1)77.8 (13.5)
Body mass index; kg.m−229.6 (5.4)29.0 (4.0)29.6 (4.4)
Indication for surgery
Previous Caesarean 25 (86%) 23 (72%) 24 (69%)
Breech 1 (4%) 7 (22%) 7 (20%)
Other 3 (10%) 2 (6%) 4 (11%)
Table 2.  Times from insertion of the Tuohy needle to spinal injection, and from spinal injection to fixation of the catheter, surgical incision, delivery, completion of surgery and first demand for patient-controlled epidural analgesia. Values are median (interquartile range [range]).
 Lateral(n = 29)Oxford(n = 32)Sitting(n = 35)p-value
Tuohy insertion to spinal injection; s155 (98–290 [60–1860])180 (120–570 [60–2280)125 (120–300 [25–1380])0.41
Spinal injection to catheter fixation; s220 (180–240 [130–540])225 (180–245 [110–480])182 (160–280 [120–785])0.59
Spinal to surgical incision; min32 (28–36 [18–50]) 35.5 (28–41 [21–61]) 32.5 (29–36 [24–56])0.27
Spinal to delivery; min44 (38–50 [26–62])43 (39–51 [25–66])43 (36–49 [30–72])0.73
Spinal to end of surgery; min72 (60–90 [44–101])75 (65–88 [53–107])73 (63–87 [46–110])0.75
Time to first patient epidural demand; min150 (124–207 [65–526])155 (125–207 [74–366])137 (107–175 [46–405])0.23

There was a trend toward reduced total ephedrine requirement in the sitting group and a significant reduction in ephedrine requirement in this group for the period until parturients were repositioned supine with tilt, just before surgery (Table 3). Blood pressure fell following CSE anaesthesia but there was no difference between groups (Fig. 1), nor was there any difference in the volume of intravenous fluid administered (Table 3).

Table 3.  Ephedrine requirements and volume of fluid administered to parturients undergoing CSE anaesthesia for elective Caesarean section randomly assigned to the left lateral, Oxford and sitting positions. Values are median (interquartile range [range]).
 Lateral(n = 29)Oxford(n = 32)Sitting(n = 35)p-value
Total dose of ephedrine; mg30 (18–30 [6–66])21 (18–30 [6–54)18 (11–23 [6–38])0.05
Dose of ephedrine before
 repositioning for surgery; mg
21 (12–30 [6–48])18 (7.5–24 [6–48])12 (6–21 [6–42])0.04
Intravenous fluid volume; ml1200 (1000–1500 [750–2000])1100 (1000–1400 [600–2000])1100 (1000–1500 [570–2000])0.52
Figure 1.

Mean systolic blood pressure following CSE anaesthesia conducted in the lateral, Oxford and sitting position. Standard deviation is omitted for sake of clarity but was 7.3–26.3 mmHg for all groups. Mixed model analysis of variance showed there was no difference among the groups (p = 0.6421).

Time to achieve sensory block to T5 and time to achieve the highest sensory block recorded was shortest in the lateral group (Table 4 and Fig. 2). More women in the Oxford group required epidural supplementation to achieve a block to T5 (Table 4).

Table 4.  Time from spinal injection to T5 sensory block, highest block and number of women who required epidural supplementation following CSE anaesthesia for sensory level to reach T5. Values are median (interquartile range [range]) or number (proportion).
 Lateral(n = 29)Oxford(n = 32)Sitting(n = 35)p-value
Spinal to T5 block; min9 (6–13 [4–30])15.5 (9–22 [4–34])14 (9–18 [6–36])0.004
Spinal to highest block; min12 (9–15.5 [4–30])18 (11–23 [5–38])16 (11–21 [9–36])0.036
Epidural bolus for block to T51 (3%)7 (22%)1 (3%)0.012
Figure 2.

Kaplan–Meier survival curve for time to achieve sensory block to T5 in the lateral, Oxford and sitting position following CSE anaesthesia for Caesarean section; p = 0.004 for lateral vs. Oxford and sitting.

There were no differences between the groups in Apgar scores at 1 min and 5 min, or in umbilical arterial or venous pH.

Discussion

In this randomised study, sensory blockade assessed by loss of light touch was most quickly achieved after CSE anaesthesia in the lateral position; however, ephedrine requirements before re-positioning for surgery were least in the sitting position. More women in the Oxford group required epidural supplementation to achieve a T5 sensory block to light touch prior to surgery.

Variation in the design of studies investigating the influence of maternal posture on the haemodynamic and sensory effects of spinal or CSE anaesthesia make comparison difficult. Different doses of spinal agents have been administered and different maternal positions have been compared using various methods and modalities for measurement of sensory block (Table 5). Patel and colleagues [2] and Inglis et al. [3] demonstrated a faster onset of sensory block and higher incidence of hypotension (or ephedrine requirement) in women placed in the lateral position. However, Yun et al. [4] were unable to show a difference in onset of block but found a significant increase in the severity and duration of hypotension in women in a sitting position. The Oxford position has been investigated in two studies. Stoneham and colleagues compared the sitting and Oxford positions for spinal anaesthesia for elective Caesarean section and concluded that the Oxford position was superior to the sitting position due to greater haemodynamic stability and a more predictable height of block [5]. A more recent study from the same group compared the Oxford, sitting and right lateral positions using a CSE technique for elective Caesarean section. In contrast, there was no difference in the time for sensory block to reach T5 but significantly lower ephedrine requirement in the lateral group [6].

Table 5.  Methods and main findings of similar studies investigating the influence of maternal posture on onset of sensory block and haemodynamic change following CSE or spinal anaesthesia for elective Caesarean section.
StudyIntrathecal bupivacainedoseOnset time of block
and modality tested
Hypotension or requirement
for ephedrine
Supplement required
  • *

    Comparison of lateral vs. sitting position only.

  • LAT = lateral position; OX = Oxford position; SIT = sitting position.

Current study12.5 mg + fentanyl
CSE
LAT faster than (OX = SIT)
Light touch
(LAT = OX) more than SITOX more than (SIT = LAT)
Patel et al. [2]*10 mg
CSE
LAT faster than SIT
Cold
LAT more than SITSIT more than LAT
Inglis et al. [3]*12.5 mg
Spinal
LAT faster than SIT
Pinprick
LAT more than SITLAT = SIT
Yun et al. [4]*12 mg + fentanyl
CSE
LAT = SIT
Cold and pinprick
SIT more than LATLAT = SIT
Stoneham et al. [5]12.5 mg + fentanyl
Spinal
SIT faster than OX
Pinprick
SIT more than OXSIT = OX
Russell et al. [6]12.5 mg + fentanyl
CSE
OX = SIT = LAT
Light touch
(OX = SIT) more than LATOX = SIT = LAT

Our study most closely resembles that of Russell and colleagues [6]; however, there are some important differences. We positioned the women in the lateral group on their left side and then turned them to the full right lateral position after CSE anaesthesia, keeping them in this position until ready for surgery. In contrast, Russell et al. administered CSE anaesthesia in the right lateral position then turned the women to the left tilted supine position. Administering spinal anaesthesia in the left lateral position and adopting the full right lateral position without shoulder elevation does not result in a more rapid onset of block when compared with turning from the left lateral position to the supine wedged position [8]. We chose our study design to make a closer comparison between the lateral position and the Oxford position, the only difference being the slight feet-up inclination and the upward tilt of the thoracic region in the Oxford position. By adopting this design, we hoped to clarify whether minimising aortocaval compression in the full lateral position during development of the block, or sparing of upper thoracic nerve roots by using a modified lateral position, is of greater importance in achieving haemodynamic stability. We found that the Oxford position conferred no greater haemodynamic stability than the full lateral position. Shoulder elevation produced by the Oxford position may slow the onset of sensory block; however, this was no different from when the sitting position was used and more women in the Oxford group required epidural supplementation to reach our defined level of surgical anaesthesia.

We assessed the development of sensory block to touch sensation because this modality has been shown to be more reliable than pinprick or cold sensation. A block to at least T6 has been recommended for Caesarean section [9–11]. It is difficult to compare studies in which different modalities were assessed and different dermatomal levels defined as acceptable for surgery. Furthermore, even when the modality of block and dermatomal levels are similar, the method of assessment may vary. Russell has recently suggested that in normal clinical practice, testing touch with ethyl chloride spray can be considered equivalent to testing touch using a Neurotip tester (Owen Mumford, Brook Hill, Woodstock, Oxford) [11]. We chose cotton wool to assess touch because it was simple and readily available. Although all women were tested using the same technique, we cannot comment on how this compares with other methods for determining the level of block to touch.

Ephedrine requirements were lowest in women placed in the sitting position, despite this being the only group that spent time in the supine tilted position before readiness for surgery. With a CSE technique in the sitting position, local anaesthetic may accumulate in the sacral region of the dural sac as the epidural catheter is passed and secured. Spread of hyperbaric local anaesthetic by gravity may spare upper thoracic nerve roots, though subsequent placement of the mother in a supine position may increase aortocaval compression. The consequences of aortocaval compression might be reduced by placing women in the lateral position following performance of CSE anaesthesia in the sitting position. Mendonca and colleagues compared CSE anaesthesia in the sitting position, followed by 2 min in the full right lateral position, before allocation to either the left lateral position or the tilted supine position [12]. They found that mothers in the lateral position had lower ephedrine requirements before repositioning for surgery. More recently, Lewis et al. [13] repeated this positioning sequence without the intermediate step of placing women in the right lateral position and found no difference in hypotension or ephedrine requirements but a slower onset of sensory block in women placed in the left lateral position after CSE in the sitting position. We are unable to comment on whether adopting these positioning sequences might further reduce the ephedrine requirements we observed in women in the sitting group. It should be noted that the difference in ephedrine requirements we observed was small, and only statistically significant from the time of spinal injection to start of surgery. Without adjusting for multiple comparisons, this finding is susceptible to type-II error.

A recurring weakness of studies investigating maternal posture and neuraxial anaesthesia, the current study included, is failure to blind observers. Due to obvious visible differences in maternal postures and the need to assess sensory block in these positions, we were unable to devise a method in which observers were unaware of the group allocation. In an attempt to limit potential bias, a second investigator who took no part in administering CSE anaesthesia assessed the development of sensory block and recorded changes in blood pressure and ephedrine usage.

The preferred maternal posture for providing spinal and CSE anaesthesia varies among anaesthetists and lack of familiarity with certain maternal positions might influence their performance. It has been argued that the sitting position facilitates the technical aspects of performing an epidural by making the midline easier to identify [14]. All anaesthetists who took part in this study were experienced in providing CSE anaesthesia in both the lateral and sitting positions; however, the majority favoured the sitting position and no anaesthetist had previous practical experience of the Oxford position. Difficulties with turning women in the Oxford position from left to right lateral and then supine have been highlighted [15] and at times we found this technique cumbersome. Though we followed Carrie's [7] original description of the Oxford position, inexperience in this technique may have created bias. We believe, however, that if a technique has a useful role, it should be reproducible in institutions other than where it was originally described and is commonly performed. Although more women in the Oxford group required epidural supplementation for the block to reach T5, we are unable to decide whether this was due to our technique or to the Oxford position itself. In addition, given that there was no difference among groups in times from spinal insertion to skin incision, delivery and completion of surgery, the significance of this in the elective situation is uncertain. Overall, however, we can conclude that the Oxford position has no advantage over the sitting or left lateral positions for CSE anaesthesia for elective Caesarean section.

Acknowledgements

Dr M. W. M. Rucklidge was supported by the Abbott Women and Infants Research Foundation. We wish to thank Research Nurses Tracy Bingham and Desire Osgood for their assistance in collection of data, Sharon Evans for help with statistical analysis and all the staff of the Department of Anaesthesia and Pain Medicine, King Edward Memorial Hospital for Women, for their co-operation.

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